Hello everyone,
I want to do an in-place tanh: y = tanh(x) assuming that y and x are
preallocated (both are Array{Float64, 1024*1024}).
I tested different implementations and got very different performance.
Version1:
julia> @time map!(tanh, y, x)
0.149988 seconds (3.15 M allocations: 48.000 MB, 1.24% gc time)
Version2:
julia> @time for i = 1:length(x)
y[i] = tanh(x[i])
end
0.355105 seconds (5.24 M allocations: 95.984 MB, 1.83% gc time)
Version3: this one is not in-place, however it's the fast one.
julia> @time y += tanh(x)
0.045402 seconds (10 allocations: 16.000 MB, 6.37% gc time)
It's quite counterintuitive for me that version1 and version 2 are much
slower than version 3.
Can someone explain this a bit?
Thanks!
Cheng
